1. Field of the Invention
The present invention relates to an ophthalmoscope, particularly to a contact-type ophthalmoscope.
2. Description of the Prior Art
The ophthalmoscope is an instrument for inspecting the fundus of an eyeball, including the retina, the optic disc, and the vasculature. However, the conventional non-contact-type ophthalmoscope is limited by the pupil and has a smaller observation area, normally only having a half-viewing angle of about 20 degrees. If the non-contact-type ophthalmoscope requires a larger observation area, the imaging system and illumination system thereof need special designs, such as enlarged lenses or an independent illumination system. However, the special design makes it difficult to reduce the volume of the non-contact-type ophthalmoscope. Since observation of the contact-type ophthalmoscope is performed close to the pupil, a larger observation area is thus obtained.
A conventional contact-type ophthalmoscope adopts an illumination system coaxial with the imaging system. However, it is difficult for the system to avoid the central reflected light from the lenses resulted in influenced observation. Further, the illumination range of the system is proportional to the size of lenses. Therefore, the system has to adopt larger lenses to achieve a larger illumination field. Another conventional contact-type ophthalmoscope adopts optical fibers for conducting light for illumination. It is understood that, due to a smaller light output angle of the optical fiber, it requires a plurality of optical fibers at different directions to provide a larger illumination field but results in complicated structure and increased fabrication cost. Further, the coupling of the light sources and the optical fibers also affects the utilization efficiency of the light source.
Accordingly, it is now a current goal to provide a larger illumination field for the contact-type ophthalmoscope with a simple structure.